1. Field of the Invention
The present invention relates generally to an under reaming pile bore excavating bucket and the method of excavating an under reamed part of a pile bore, and more particularly to an excavating bucket such that an under reamed part of a pile bore can be excavated and further the excavated soil can be moved into the bucket body for easy removal of soil. The bucket includes, in particular, a plurality of slidable wing bits housed within a bucket and moved downward and extended outward along guide rails at the bottom of an already excavated straight pile bore.
2. Description of the Prior Art
In executing pile foundations in construction works, a method of drilling earth (earth drill method) is conventionally adopted. In this earth drill method, a rotatable bucket is used for excavating a straight pile bore and moving the excavated soil from the excavated bore to the outside. The bucket is attached to the lowermost position of a kelly rotatably suspended by a crane. The bucket includes a bottom plate provided with a plurality of drill bits. When the bucket is rotated by the kelly, the soil excavated by the drill bits are taken into the bucket. The bucket filled with the excavated soil is raised by the crane and the soil in the bucket is removed by opening the bottom plate thereof.
By the way, as an economical method of executing pile foundations, an under reamed bore foundation is well known, in which a larger diameter bore is excavated at the bottom of a straight pile bore to increase the pile end bearing capability against a vertical load applied to the pile.
In the earth drill method using a bucket, however, it is rather difficult to realize an under reaming pile bore excavating bucket of simple configuration and a method of executing the same in simple steps.
A more detailed description of the prior-art pile bore excavating bucket will be made hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE INVENTION.